build fix for mac os:

1) type_info visibility for CatapultAttack
2) using IObjectInfo::CArmyStructure in min_element : operator< should be const

lib/NetPacks.h

@@ -1516,7 +1516,7 @@ struct ObstaclesRemoved : public CPackForClient //3014
 };
 
 //FIXME: figure out why gcc fails to find type_info for this class with -fvisibility=hidden flag set
-#ifdef __linux__
+#if defined(__linux__) || defined(__APPLE__)
 struct DLL_LINKAGE CatapultAttack : public CPackForClient //3015
 #else
 struct CatapultAttack : public CPackForClient //3015

lib/mapObjects/CObjectClassesHandler.h

@@ -65,7 +65,7 @@ public:
 			walkersStrength(0)
 		{}
 
-		bool operator <(const CArmyStructure & other)
+		bool operator <(const CArmyStructure & other) const
 		{
 			return this->totalStrength < other.totalStrength;
 		}